Pipe lines used in industries, such as petroleum extraction, may be long and exposed to alternating cycles of heating and cooling. This is of particular concern for above-ground pipe lines, which are subjected to larger temperature variation than below ground lines. The heating and cooling may be the result of large variations in ambient temperature, both daily and seasonal, to which the pipe line is exposed, as well as due to the heat contained in the fluid being pumped through the pipe line. The fluid itself may be hot, or may be heated by pumping action. Friction between the fluid and pipe line may also contribute to the heating and expansion.
As is well known, many materials, especially metals such as steel from which pipe lines are often constructed, expand and contract in response to heating and cooling. The coefficient of linear expansion of the material is the characteristic which quantitatively describes how an elongate item, such as a pipe element, will behave in response to heating and cooling. The units of the coefficient of linear expansion, specified in English units of measure, are inches of expansion per inch of pipe per temperature change in degrees Fahrenheit. It is thus clear that expansion or contraction of a pipe line will be directly proportional to both the change in temperature as well as the length of the pipe line.
For long pipe lines subjected to even small ambient or internal temperature variations it is advantageous to provide expansion joints at intervals along the length of the pipe line to accommodate the thermally induced changes in length and prevent damage to the pipe line which might otherwise occur. For example, the pipe line may buckle when subjected to compression due to expansion in response to an increase in temperature, or, a joint may fail when subjected to tension loads due to pipe line contraction in response to a decrease in temperature.